The invention generally relates to supply voltage identification.
A typical computer system includes a power supply that provides and regulates various supply voltages that are used by the components of the computer system. As examples, the computer system may provide and regulate supply voltages for 5 volt (V), 3.3 V, 2.5 V, 1.8 V and 1.5V supply lines, or power planes, of the computer system.
One component that receives supply voltages from the voltage planes of the system is a central processing unit (CPU) device. In this manner, the CPU device may be encoded with a voltage identification (VID) number, a digital number that identifies a specific supply voltage to be furnished to the core circuitry of the CPU device. To derive the VID number for a particular CPU device, the device is tested to determine an optimal supply voltage for its core circuitry. Based on this determined optimal supply voltage, the VID number may be encoded into the CPU device.
One way to encode the VID number involves configuring the packaging of the CPU device so that external terminals of the device indicate the VID number. For example, the CPU device may be packaged in a ball grid array package, a package that houses the die that contains the core circuitry of the CPU device and includes specific external solder terminals, or bumps, that indicate the VID number. A conventional technique to encode a particular VID number into the CPU device is to selectively connect the VID-associated external solder bumps together inside the package in a specific configuration to indicate the VID number. Therefore, due to this technique, each different VID number requires a different package configuration.
As an example, FIG. 1 depicts a system 10 that includes a CPU device 12 that is encoded with a VID number using the technique that is described above. At power up of the system 10, the CPU device 12 furnishes a digital signal (called VID[4:0]) that indicates its VID number to a digital-to-analog converter (DAC) 13. In response to the VID number, the DAC 13 furnishes an analog reference voltage (called VREF) that forms an analog indication of the VID number. A voltage regulator 14 receives the VREF voltage and in response generates a supply voltage (called VCC) for the CPU device 12 that is near the supply voltage level that is indicated by the VID number.